1. Field of the Invention
This invention relates to the production of temperature-resistant, compact or cellular polyurethane urea elastomers by the reaction injection molding technique using high-melting aromatic diaminodiphenyl ureas.
2. Description of the Prior Art
The production of compact or cellular polyurethane elastomers from polyisocyanates and relatively high molecular weight polyhydroxyl or polyamino compounds in the presence of catalysts and, optionally, chain-extending agents, crosslinking agents, blowing agents, and other auxiliaries or additives is known. Provided the starting components are suitably selected, it is possible by this process to produce both elastomeric and rigid products and intermediate variants.
However, systems containing diamines as chain-extending agents could only be used for the production of optionally cellular elastomeric moldings having a compact skin after the development of the high-pressure reaction injection molding technique. Diethyl toluenediamines and similar aromatic diamines, wherein the amino groups are sterically hindered by alkyl substituents in the ortho position, are largely used for this purpose.
Processes for the production of polyurethane elastomers using polyamines as chain-extending agents are described, for example, in DE-A-No. 2,622,951 (U.S. Pat. No. 4,218,543) and in EP-A-Nos. 0,081,701, 26,915 and 69,286.
Despite the stearic hindrance, however, the amino groups are still sufficiently reactive that the cream times of the corresponding systems are of the order of a few seconds. For this reason, considerable difficulties are involved in filling large and/or complicated mold cavities and in obtaining products of relatively high flexural strength by increasing the quantity of amine chain-extending agents. In the latter case, useless products which break on removal from the mold have previously been obtained beyond a certain quantity of diamine.
The moldings obtained by the known processes are used, for example, in the shoe industry as soles or in the automotive industry as body or fascia components.
There is a need for chain-extending agents which may be used for the production of formulations for reaction injection molding (RIM) which have an adequate cream time for filling large molds, have short in-mold times for sufficiently short cycle times, show acceptable properties (green strength, etc.) at the time of removal from the mold and after hardening, show excellent physical and thermal properties such as high flexural strength and heat deflection temperature under load.
The use of mixtures of aromatic diamines having different reactivities are described for this purpose in U.S. Pat. No. 4,631,298, although their gel times are still of the order of a few seconds.
An object of the present invention is to provide systems using aromatic diamines as chain-extending agents which are suitable for the production of optionally cellular elastomers by reaction injection molding, wherein the systems have cream times such that large molds can be readily filled and such that processing may be carried out by the low-pressure process almost exclusively used in the shoe industry. It is a further object of the present invention to obtain adequate cycle times and also products which have good green strength and excellent physical properties after hardening.
According to the invention, this object is surprisingly achieved by using high-melting p- and/or m-diaminodiphenyl ureas as heterogeneous chain-extending agents for the production of the polyurethane urea elastomers.
The use of solid diamines as heterogeneous chain-extending agents is known per se. Thus, U.S. Pat. No. 3,105,062 uses solid diamines in polyurethane systems which are hardened below their melting point in heterogeneous phase. However, this process is exclusively used for the production of cast elastomers by the prepolymer technique; the patent specification expressly points out and provides an example to show that completely useless products are obtained in a one-shot process in which polyol, polyisocyanate and solid diamines are mixed together and then hardened in a single step.
Finally, DE-OS No. 2,635,400 describes heterogeneous systems having long pot lives using solid diamines which are preferably processed by the prepolymer technique. However, the preferred o-diaminodiphenyl urea is too unreactive to isocyanates, such that this compound is totally unsuitable as a chain-extending agent for rapid one-shot systems.
Accordingly, it was completely surprising to find that homogeneous polyurethane urea elastomers combining excellent mechanical properties with adequate green strength can be obtained by the reaction of liquid polyisocyanates with combinations of special p- and m-diaminodiphenyl ureas and relatively high molecular weight polyhydroxyl or polyamino compounds in a heterogeneous one-shot reaction using the reaction injection molding technique.
The homogeneity of the products obtained by this process is particularly surprising because it had been expected that useless elastomers containing gel particles would be formed when reactants in powder form are reacted in a heterogeneous reaction by a one-shot process.